The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical piezoelectric pump includes a piezoelectric actuator stack located within a pump housing. The piezoelectric stack is composed of a piezoelectric material that, when subjected to an electric voltage, expands and contracts in shape and/or size as compared to its normal condition when no voltage is applied. The actuator stack is operable to engage a diaphragm located within a fluid chamber. The fluid chamber communicates with a one-way inlet valve and with a one-way outlet valve. When an electric voltage is applied to the actuator stack, the materials within the actuator stack expand and contract. This displacement is applied to the diaphragm within the fluid chamber. Accordingly, the displacement of the diaphragm varies the volume of the fluid chamber which draws hydraulic fluid in through the inlet valve and forces the hydraulic fluid out through the outlet valve.
These conventional piezoelectric pumps are capable of producing a strong displacement force, which provides high hydraulic pressure within the fluid chamber. However, the actual amount of displacement of the piezoelectric material within the actuator stack is limited. Accordingly, these typical piezoelectric pumps are not able to provide high hydraulic fluid flow, which in turn limits the applications suitable for piezoelectric pumps. For example, it would be desirable to employ a piezoelectric pump within a transmission hydraulic control system in order to provide pressurized hydraulic fluid flow when the engine is turned off. This application may be especially desirable in hybrid powertrains. However, conventional piezoelectric pumps are not capable of providing the high fluid flow required by transmission hydraulic control systems. Accordingly, there is a need in the art for a piezoelectric pump that is operable to provide a high flow of hydraulic fluid.